Embryogenic callus was obtained from leaf sheath explants on MS supplemented with 16.56 μM picloram in Musa acuminata (diploid) cv. Njalipoovan (AB). Exogenous application of ascorbic acid on somatic embryogenesis at optimal level accelerated the conversion rate of the embryos. Shoot and root developed from the embryos on MS incubated in dark. Further growth of plantlets obtained on half strength of MS under light conditions. Regenerated plantlets showed 100% survival.India has a rich genetic diversity of banana with more than 90 distinct clones. South India is well-known for the presence of numerous diploid as well as triploid edible banana cultivars (Heslop-Harrison and Schwarzacher 2007). Local or indigenous cultivars are generally more tolerant to local conditions and have lesser growth requirements to obtain satisfactory yield. Because of high sterility and polyploidy of the edible varieties (Stover and Simmonds 1987), conventional breeding is difficult in banana. The food value of bananas has been appreciated for a long time and continuous efforts are made to broaden the research on production of improved varieties. However, parthenocarpy, female sterility, polyploidy in different cultivars and limited amount of genetic and genomic information make the production of new banana cultivars difficult and time consuming. The alternative techniques such as tissue culture has been attempted in order to induce variations in banana plants and to select variants having desired qualities (Novak et al. 1989). Somatic embryogenesis was achieved using floral explants (Panis et al. 1993, Navarro et al. 1997 or cell suspensions of diploid and triploid cultivars with AA, AAA, AAB and ABB genomes (Cronauer and Krikorian 1983, Escalant and Teisson 1988, Ganapathi et al. 2001. Establishment of somatic embryogenesis has a great potential for overcoming some of the factors that limit traditional approaches to banana and plantain improvement.
Somatic embryogenesis receptor kinase (SERK) gene is known to be a marker of somatic embryogenesis in several plant species. The present study reported the presence of SERK gene from bract derived embryogenic calli bearing somatic embryos. The analysis of the expression pattern of the SERK gene during embryogenic cell formation and somatic embryogenesis revealed that SERK expression continued during pro embryogenic mass formation. In the present study the amplified product of cDNA from the somatic embryos has molecular size 1459 bp. The non-embryogenic callus also showed the presence of faint bands. In all the samples the amplified product from β -actin primer showed bands of 650 bp with similar intensity in both the embryogenic and non-embryogenic samples.
Secondary somatic embryogenesis was observed in the suspension culture of bract-derived banana calli in the presence of liquid Murashige and Skoog medium with additives such as glutamine (0.68-34.21 µM), biotin (0.40-20.46 µM), or ascorbic acid (0.56-28.38 µM) along with malt extract (100 mg/l). After the initiation of homogenous cell suspension, fully developed somatic embryos were observed after fifth subculture in the four cultivars. Somatic embryos were successfully regenerated in basal MS medium and were transplanted after fifth week. After fifth subculture, the frequency of somatic embryos increased in each culture flask. Maximum number of somatic embryos were observed in cv. Sannachenkadali (46.12 ± 0.85 a ) when cultured in liquid MS medium supplemented with biotin (8.18 µM) along with malt extract (100 mg/l), in followed by cv. Matti (44.75 ± 1.19 a ) having (AA) genome. SEM analysis revealed the presence of secondary somatic embryos on the surface of primary somatic embryos in each culture and it attributed a high frequency of somatic embryogenesis. The addition of biotin along with malt extract increased the frequency of secondary somatic embryogenesis in the diploid banana cultivars.
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